Subleading power corrections for event shape variables in e + e - annihilation.

We consider subleading power corrections to event shape variables in e+e- collisions at the first order in the QCD coupling αS. We start from the jettiness variable τ2 and the y23 resolution variable for the kT jet clustering algorithm and we analytically compute the corresponding cumulative cross section. We investigate the origin of the different power suppressed contributions in the two-jet limit and trace it back to their different coverage of the phase space. We extend our analysis to the case of thrust and of the C -parameter, and we finally discuss a class of observables that depend on a continuous parameter giving different weight to central and forward emissions and we evaluate the corresponding subleading power corrections.